php firebase api - delete children element from nested document

I'm using php sdk to delete some fields from firestore database, i want to delete a map from an array inside a document, but instead the function used delete all maps inside the parent array.

My firestore database looks like this

What i'm trying to do is remove a specific index ex: index 0 with it's children from imageUrls array not all the maps inside it.

I tried these 2 functions :

$usersRef->update([
        ['path' => 'imageUrls.image_url', 'value' => FieldValue::arrayRemove(['image.png'])]
    ]);

and this one

$usersRef->update([
    ['path' => 'imageUrls.image_url', 'value' => FieldValue::deleteField()]
]);

The first function remove all imageUrls childrens and change imageUrls type from array to map, while the second one nothing happened. All the fields still exist in the document and no deletion occurd

<?php 

namespace App\Services;
use Google\Cloud\Firestore\FirestoreClient;
use Google\Cloud\Firestore\FieldValue;
use Google\Cloud\Firestore\FieldPath;

class FirebaseService
{
    public function delete()
    {
        // Create the Cloud Firestore client
        $db = new FirestoreClient(
            ['projectId' => 'MyProjectId']
        );

        $usersRef = $db->collection('NewStories')->document('1');

        $usersRef->update(
                         [
                              ['path' =>'imageUrls.image_url', 
                              'value' => FieldValue::arrayRemove(['image.png'])]
                         ]);  
    }
}